Attention is focused on a virtual slide system capable of acquiring virtual slide image data by imaging a stained biological sample on a slide (also referred to as a preparation) using a digital microscope, and observing the virtual slide image data displayed on a monitor (Patent Literature 1).
In addition, there is known a technique for acquiring a plurality of layer image data items focused on different depths in a sample while changing a focus position in an optical axis direction by using a digital microscope in the case where a thick biological sample is imaged (Patent Literature 2). Three-dimensional image data constituted by the plurality of layer image data items is referred to as Z-stack image data.
Further, there is also known a technique for extracting focal point areas which are in focus from a plurality of layer image data items, and combining the focal point areas to thereby generate two-dimensional focus stacking image data which is focused on all of the areas (Patent Literature 3).
In addition, there is also known a technique for reproducing a phase distribution image by using two successive images in the vicinity of an in-focus position of an optical system (Patent Literature 4).